Question:
Which of the following pair of lanthanide elements have the same atomic radii?
Which of the following pair of lanthanide elements have the same atomic radii?
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Lanthanoid contraction is due to poor shielding by $4f$ electrons.
Updated On: Apr 27, 2026
- Lanthanum and Lutetium
- Samarium and Gadolinium
- Praseodymium and Holmium
- Terbium and Cerium
- Promethium and Dysprosium
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Concept
Lanthanoid contraction causes a steady decrease in atomic and ionic radii along the series.
Step 2: Meaning
However, certain pairs show very similar sizes due to the specific filling of the $4f$ subshell.
Step 3: Analysis
Samarium (Sm) and Gadolinium (Gd) are adjacent or near-adjacent elements where the cumulative effect of contraction is minimal between them compared to far ends of the series.
Step 4: Conclusion
According to the answer key, Samarium and Gadolinium are the designated pair.
Final Answer: (B)
Lanthanoid contraction causes a steady decrease in atomic and ionic radii along the series.
Step 2: Meaning
However, certain pairs show very similar sizes due to the specific filling of the $4f$ subshell.
Step 3: Analysis
Samarium (Sm) and Gadolinium (Gd) are adjacent or near-adjacent elements where the cumulative effect of contraction is minimal between them compared to far ends of the series.
Step 4: Conclusion
According to the answer key, Samarium and Gadolinium are the designated pair.
Final Answer: (B)
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